The relaxation of residual stress in a shot-peened high strength low alloy steel in response to applied loads has been investigated for both single-shot and cyclic loading using X-ray diffraction (first 10 μm) and fine increment hole-drilling to yield depth profiling. The compressive residual stress showed a peak at about 50 μm below the surface. Under single-shot compressive loading, relaxation became significant when the combined surface and applied compressive stresses exceeded the proportional limit of the unpeened surface. The steel showed good resistance to residual stress relaxation under cyclic loading conditions, with only a 13% decrease despite cyclic load amplitudes at 50% of the 0.2% proof stress in compression. Whilst large single-shot or cyclic stresses would represent rare occurrences, their impact on residual stress relaxation should be accounted for in structural integrity assessment.
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